1. Field of the Invention
The present invention relates to biocidal compositions, particularly those containing a synergistic mixture of carbamate and organotin biocides useful for protecting materials exposed to an aquatic environment. This invention especially relates to the prevention and inhibition of fouling of marine structures such as boat, ship, or other vessel hulls, pilings, oil well drilling towers, and the like by organisms commonly found in sea water.
In a preferred embodiment, the present invention relates to a biocidal composition containing a synergistic mixture of carbamate and tributyltin biocides. In this preferred embodiment, a marine structure is treated by coating the surface thereof with a paint containing an organic binder and a biocidally effective amount of the mixture of (1) the carbamate compound, such as one selected from the group consisting of 3-iodo-2-propynyl propyl carbamate, 3-iodo-2-propynyl butyl carbamate, 3-iodo-2-propynyl hexyl carbamate, 3-iodo-2-propynyl cyclohexyl carbamate, 3-iodo-2-propynyl phenyl carbamate, 3-iodo-2-propynyl benzyl carbamate, 4-iodo-3-butynyl propyl carbamate and mixtures thereof, and (2) the tributytin compound, such as one selected from the group consisting of bis(tributyltin) oxide, tributyltin fluoride, tributyltin methacrylate, tributyltin phosphate and tributyltin naphthenate, and mixtures thereof. In another embodiment, a marine structure is treated by coating its surface with a composition containing a biocidally effective amount of either 3-iodo-2-propynyl propyl carbamate or 4-iodo-3-butynyl propyl carbamate or a mixture thereof.
2. Description of Related Art
Singer U.S. Pat. No. 3,923,870 describes urethanes of 1-halogen-substituted alkynes and their fungicidal activity. The compound 3-iodo-2-propynyl butyl carbamate (IPBC) (CAS 55406-53-6) described in U.S. Pat. No. 3,923,870 is widely used as a fungicide for aqueous and organic solvent based systems such as paints and coatings, metal cutting fluids, textile and paper coatings, inks, plastics, adhesives and the like. Research indicates that IPBC has a promising efficacy profile against wood destroying organisms (fungi), having shown low toxic values for common fungi. Indeed, a unique characteristic of IPBC is its efficacy against both blue stain (ascomycetes) and general wood destroying fungi (basidiomycetes) at a reasonable application rate. IPBC is also known as an algicide for use in fresh water and marine applications, see U.K. Patent 2,138,292.
It also is known that organic tin compounds such as those of the general formula: EQU (CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2).sub.3 Sn-R.sup.4
where R.sup.4 is selected from (CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2).sub.3 SnO, fluoride, chloride, phosphate, acrylate methacrylate, naphthenate, hydroxide, octoate, phthalate, sulfate, maleate, fumarate, laureate, linoleate, abietate, ethanesulphonate, and the like can be used in paints to provide anti-fouling property to coatings applied to ship hulls to prevent fouling by algae and other marine organisms (pests).
The prior art, however, does not provide any indication whether the combination of the fungicide IPBC or other related carbamate fungicides with an organic tin compound such as one or more of the above-mentioned tributyltin-type compounds would be useful for anti-fouling coatings for protecting materials exposed to an aquatic (eg. marine) environment, such as ship hulls and other underwater constructions.
The growth of marine organisms on the submerged parts of a ship's hull increases the frictional resistance of the hull to passage through water, leading to increased fuel consumption and/or a reduction in the speed of the ship. Marine growths accumulate so rapidly that the remedy of cleaning and repainting as required in drydock is generally considered too expensive. An alternative which has been practiced with increasing efficiency over the years, is to limit the extent of fouling by applying to the hull a top coat paint incorporating anti-fouling agents. The anti-fouling agents are biocides which are freed from the surface of the paint over a period of time at a concentration lethal to marine organisms at the hull surface. The anti-fouling paint fails only when the concentration of biocide available at the paint surface falls below the lethal concentration and with modern paints up to two years of useful life is expected.
There are marked distinctions between the requirements for biocides in different environments, such as antifungal agents in house paints, fresh water algicides, and antifouling agents for marine structures exposed to sea water flora and fauna. As is known, the mildew or fungus which grows on house paints and the like, utilizes the paint medium as a nutrient, or in some cases, the underlying substrate, such as wood, as the nutrient. The mycelia and fruiting bodies of the fungi contact or penetrate the paint film and thus, through intimate contact with any fungicides in the film (to a large extent regardless of whether the fungicides are highly soluble, slightly soluble, or insoluble in water), the fungi are destroyed. In cooling towers utilizing fresh water, slime and algae may develop if effective compounds for combatting their growth are not present. In the case of cooling tower water, the compound should be highly soluble. In paints such as exterior house paints, undergoing normal exposure to weather, the solubility of the compound is not as critical since the paint film is only sporadically exposed to liquid water.
While IPBC and related carbamate compounds are known to exhibit good fungicidal and algicidal activity, it is not known whether these fungicides could also be used in anti-fouling coatings in combination with known organic tin compounds, particularly tributyltin-type compounds, to prevent the growth of marine organisms like algae, barnacles, encrusting bryozoan, tunicates, hydroids, adherent slime or other higher developed crustaceas on submerged surfaces. Results obtained with anti-fouling paints when utilizing IPBC and related compounds are not predictable from their effectiveness as general biocides, whether against bacteria, fungi, insects, etc. It also is not known if or how long the combination would retain its efficacy as an anti-fouling biocide formulation or whether it might even be superior in overall performance as an anti-fouling compound in comparison to the iodopropynyl carbamate-related compounds or the tributyltin-related compounds by themselves.
Additionally, it is not known how the combination of one or more members from each group of these compounds would affect their overall biocidal (anti-fouling) activity, for example, if used in paint to protect ship hulls from the growth of marine organisms. As is always a possibility when using a combination of chemicals having diverse activities, one of the chemicals may impair or interfere with the activity of the other.
From the foregoing, it is apparent that the effectiveness of biocidal materials useful in combatting fungi, insects, bacteria, and the like in non-aqueous media, and biocides effective in combatting fungi, slime, and algae in fresh water systems, cannot be used to predict the effectiveness of these compounds as anti-fouling agents in sea water and brackish water capable of supporting marine life such as barnacles, slime, hydroids, "grassy" brown felt algae and the like.
Since the prior art has not disclosed or suggested combining IPBC or its related carbamate compounds with organic tin compounds, and especially the above-mentioned tributyltin-type biocides, the prior art does not indicate what amounts of the fungicide IPBC (and its related carbamate compounds) and of the organic tin compound, such as one or more of the above-noted tributyltin-type biocides, are required to provide an optimum in anti-fouling application against algae and higher developed marine organisms. For similar reasons, it is not known what amounts of IPBC (and its related carbamate compounds) and of the organic tin compound are needed to obtain the long-lasting efficacy needed for successful anti-foulant, marine applications, or how to formulate an effective anti-foulant composition using this biocide combination.
In this regard, there is a growing concern about the environmental effects caused by using the organic tin biocides at their present commercial levels as an anti-foulant active ingredient in coating compositions for aquatic (marine) applications. It has been shown that, due to the wide-spread use of tributyltin-type compounds in particular, at concentrations as high as 20 wt. % in paints for ship bottoms, the pollution of surrounding water due to leaching has reached such a level as to cause the degradation of mussel and shell organisms. These effects have been detected along the French-British coastline and a similar effect has been confirmed in U.S. and Far East waters. Under the most recent regulatory restrictions, with limited exceptions, pleasure boats up to 25 meters long are no longer permitted to use anti-foulant paint containing high levels of tributyltin compounds.
Research has shown that as long as the leaching rate of tin can be maintained at or below about 4 ug/cm.sup.2 per day, aquatic life does not appear to be affected over the long term. However, it has also been found that to be effective for controlling marine algae, as well as higher developed marine organisms, from the painted surface of ship bottoms, a certain minimum leaching rate of tin of about 9 to 16 ug/cm.sup.2 /day is required. Usually, this higher leaching rate is achieved with a concentration of tributyltin compound at about 15% to 20% by weight of paint.
Obviously, these two requirements are at odds. Authorities have reluctantly agreed that as long as there is no satisfactory substitute for the anti-foulant organic tin active ingredients, larger ships, i.e., those above a length of 25 meters, are still permitted to use such compounds to minimize fouling. As an indication of the importance of new solutions to this age old problem, the EPA has agreed to certify within 90 days new anti-foulant paints meeting the requirements of acceptable release rates.